Thin film keypad and method of making same

ABSTRACT

A thin film keypad includes a retainer sheet and a plurality of keycaps molded onto keycap attachment regions on the retainer sheet such that the keys are mechanically secured to the retainer sheet. The retainer sheet is made of a thin film material, such as polycarbonate or polyester, and each keycap attachment region includes at least a hole and/or at least one retainer anchor portion. The keycaps are molded from a plastic material, such as polycarbonate or polyester, ABS or a polycarbonate/ABS blend. The thin film material is placed in a molding tool and the plastic material is injected into a keycap mold cavity such that the plastic material flows through the holes and/or around the retainer anchor portions, thereby anchoring the keycaps to the retainer sheet.

TECHNICAL FIELD

[0001] The present invention relates to keypads and molding techniquesand more particularly, relates to a thin film keypad and method ofmaking the thin film keypad.

BACKGROUND INFORMATION

[0002] Electronic devices, such as wireless telephones, have drasticallyreduced in size. These devices include keypads that must also be reducedin size. In particular, the manufacturers of these electronic deviceshave demanded that the keypads be extremely thin. Attempts at reducingthe size and thickness of these keypads have met with variousdifficulties.

[0003] According to one method of constructing thin keypads, the keysare adhered to a plastic film. However, the keys often would not adhereadequately, especially if the keys and film are made of differentmaterials (e.g., keys made of ABS and film made of polycarbonate orpolyester).

[0004] Another method of making keypads is the insert mold design (IMD)technique. According to this technique, a cavity is formed in the filmand the key is molded into the cavity. As a result, however, the film ison the outside of the keypad and graphics are printed on the film. Onedisadvantage of keypads made using the IMD technique is the limitedextent to which the film can be stretched while retaining graphicquality. The dimensions of the keys (i.e., the height) made using theIMD technique are also limited.

[0005] Accordingly, there is a need for a thin film keypad where thekeys will remain secured to a top surface of the thin film, even whenmaterials are used that do not adhere together well.

SUMMARY

[0006] In accordance with the needs addressed above, the presentinvention provides a thin film keypad and method of making same.According to one aspect of the present invention, the thin film keypadcomprises a retainer sheet made of a thin film material and having a topand bottom surface. The retainer sheet includes at least one holeextending through the thin film material and at least one retaineranchor portion formed from a portion of the thin film material extendingupwardly from the top surface. At least one keycap is molded onto a topsurface of the retainer sheet and around the retainer anchor portion.The keycap includes a keycap anchor portion molded through the hole inthe thin film material such that the keycap anchor portion and theretainer anchor portion mechanically secure the keycap to the retainersheet.

[0007] According to another aspect of the present invention, the thinfilm keypad comprises a retainer sheet made of a thin film material andhaving a top and bottom surface. The retainer sheet includes a pluralityof keycap attachment regions. Keycaps are molded onto a top surface ofthe retainer sheet at respective keycap attachment regions. The keycapsare molded around portions of the thin film material such that thekeycaps are mechanically secured to the retainer sheet.

[0008] According to one embodiment, the thin film material is preferablya plastic material, such as polycarbonate or polyester, having athickness in a range of about 0.005 in. (0.127 mm) to 0.010 in. (0.254mm). The keycap is preferably made of a plastic material, such aspolycarbonate, polycarbonate/ABS blend, or ABS.

[0009] One embodiment of the retainer sheet includes holes extendingthrough the thin film material at the keycap attachment regions. Theportions of the thin film material around which the keycaps are moldedinclude edges of the thin film material around the holes. The portionsof the thin film material around which the keycaps are molded alsoinclude flaps cut out from the thin film material and extending upwardlyfrom the top surface.

[0010] According to further aspect of the present invention, a method ofmaking a thin film keypad comprises forming at least one keycapattachment region on a thin film material with each keycap attachmentregion including at least one molding material passage region. The thinfilm material is placed into a molding tool having at least one keycapmold cavity such that each molding material passage region is locatedwithin each keycap mold cavity, respectively. A molding material isinjected through the molding material passage region in the thin filmmaterial and into the keycap mold cavity such that at least one keycapis molded onto a top surface of the thin film material. The moldingmaterial flows around a portion of the thin film material such that thekeycap is mechanically secured to the thin film material. The outline ofthe retainer sheet can then be cut from the thin film material such thatthe keys are molded onto the retainer sheet.

[0011] In one preferred method, forming each keycap attachment regionincludes forming at least one hole through the thin film material. Theretainer sheet is placed in the molding tool with the hole positionedbetween the keycap mold cavity and an anchor mold cavity such that themolding material flows through each hole and around an edge of the thinfilm material. Forming the keycap attachment region also preferablyincludes cutting at least one flap from the thin film material to formthe material passage region. The molding tool preferably includes a gatefor injecting the molding material. Inserting the retainer sheet intothe molding tool preferably includes inserting the gate through thematerial passage region such that the gate moves the flap into thekeycap mold cavity. The molding material flows around each flap.

[0012] According to a further aspect of the present invention, a methodof making a thin film keypad comprises forming a plurality of keycapattachment regions on a thin film material such that each keycapattachment region includes at least one hole and at least one materialpassage region. The thin film material is placed into a molding toolincluding a female side having keycap mold cavities and a male sidehaving anchor mold cavities. The retainer sheet is positioned such thatthe holes are located between respective keycap mold cavities and anchormold cavities and such that the material passage regions are locatedwithin respective keycap mold cavities. A molding material is injectedthrough the material passage regions in the thin film material and intothe keycap mold cavities. The molding material flows through the holesand into the anchor mold cavities such that keycaps are molded onto atop surface of the thin film material and are mechanically secured tothe thin film material.

[0013] According to one method, forming the material passage regionsincludes cutting flaps from the thin film material. According to anothermethod, forming the material passage regions includes forming formedhole portions from the thin film material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features and advantages of the present inventionwill be better understood by reading the following detailed description,taken together with the drawings wherein:

[0015]FIG. 1 is a plan view of a thin film keypad, according to oneembodiment of the present invention;

[0016]FIG. 2 is a side cross-sectional view of a thin film keypad,according to one embodiment of the present invention;

[0017]FIG. 3 is a plan view of a thin film material used to form aretainer sheet, according to one method of the present invention;

[0018]FIG. 4 is a plan view of the thin film material having keycapattachment regions formed thereon, according to one method of thepresent invention;

[0019]FIG. 5 is an enlarged plan view of a flap formed in the retainersheet, according to one method of the present invention;

[0020]FIG. 6 is a side cross-sectional view of the flap formed in theretainer sheet;

[0021]FIG. 7 is a cross-sectional view of a molding tool having aretainer sheet placed therein, according to one method of the presentinvention;

[0022]FIG. 8 is a cross-sectional view of a key molded onto the retainersheet, according to one embodiment of the present invention;

[0023]FIG. 9 is an enlarged cross-sectional view of a formed holeportion, according to an alternative embodiment of the presentinvention; and

[0024]FIG. 10 is a cross-sectional view of a key molded onto theretainer sheet, according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] A thin film keypad 10, FIG. 1, according to one embodiment of thepresent invention, includes a retainer sheet 20 and keycaps 26 securedto the retainer sheet 20. The exemplary thin film keypad 10 is designedfor use in a wireless telephone, as well as other applications. Keypadsmade according to the present invention, however, can have other shapes,designs and layouts for use in other types of devices. Although the thinfilm keypad 10 is shown with a certain number of keycaps 26, any numberof keycaps 26 can be secured to the retainer sheet 20.

[0026] As shown in greater detail in FIG. 2, the retainer sheet 20 hastop and bottom surfaces 22, 24. The keycaps 26 are preferably moldedonto the top surface 22 of the retainer sheet 20 such that the materialof the keycaps 26 is molded around a portion of the retainer sheet 20,as will be described in greater detail below. The preferred embodimentof each keycap 26 includes at least one keycap anchor portion 30extending through and engaging the bottom surface 24 of the retainersheet 20. The keycap anchor portion 30 also acts as an actuator in thewireless telephone or other device in which the keypad 10 is used. Thepreferred embodiment of the retainer sheet 20 includes at least oneretainer anchor portion 32 extending into the material of each keycap26.

[0027] The exemplary embodiment shows two retainer anchor portions 32extending into each of the keycaps 26 and one keycap anchor portion 32extending from each of the keycaps to securely anchor the keycaps 26.However, any number of retainer anchor portions 32 can extend into thekeycap 26 and any number of keycap anchor portions 30 can extend fromthe keycap 26. The center keycap 26 a shown FIG. 1, for example,includes two keycap anchor/actuator portions 30 without any retaineranchor portions 32. According to a further alternative, the keycap 26can be secured using only retainer anchor portions 32 without any keycapanchor/actuator portions 30.

[0028] The retainer sheet 20 is made of a thin film material andpreferably a plastic, such as a polycarbonate or polyester material. Thekeycaps 26 are also preferably made of a plastic material, such aspolycarbonate, ABS, or a polycarbonate/ABS blend. Other types ofmaterials are also contemplated for the retainer sheet 20 and keycaps26.

[0029] Referred to FIGS. 3-7, one method of making the thin film keypad10 is described below. The retainer sheet 20 is formed from a thin filmmaterial 36 (FIG. 3). The thin film material 36 is preferably a plasticmaterial, such as polycarbonate or polyester, having a thickness in therange of about 0.005 in. (0.127 mm) to 0.010 in. (0.254 mm). and mostpreferably about 0.005 in. One example of the thin film material is ahigh stability polycarbonate known as type T2F, which is available fromGE Plastics. Other thermally stabilized films are also appropriate forthis process. The thin film material 36 preferably includes registrationholes 38 punched through the thin film material 36 for tool pinningregistration.

[0030] The thin film material 36 is die cut to form keycap attachmentregions 40 (FIG. 4). Each keycap attachment region 40 includes at leastone hole 42 cut through the thin film material 36. Each keycapattachment region 40 also includes at least one molding material passageregion 43 (e.g., a gate location) through which the molding material isinjected, as described in greater detail below. In one embodiment, aflap 44 (FIGS. 5 and 6) is cut out from the thin film material 36 tocreate the material passage region 43. The flap 44 preferably has sidestapering inward toward the hinge such that the end of the flap is wider.This tapered design allows the flap 44 to anchor more securely in thekeycap 26 and prevents the flap 44 from sliding out of the keycap 26.One example of the flap 44 is about 0.035 in. (0.889 mm) long.

[0031] Although the exemplary embodiment shows one hole 42 and two flaps44 formed in each keycap attachment region 40, any number of holes 42and/or flaps 44 can be formed depending upon the desired number ofkeycap anchor portions 30 and/or retainer anchor portions 32. Also, theholes 42 and/or flaps 44 can be formed with various positions andorientations. In another embodiment, for example on the keycapattachment region 40 for the center keycap 26 a, the material passageregion 43 a (e.g., the gate location) can be formed without a flap.Alternatively, the keycap attachment region 40 can be formed with flaps44 but no holes 42.

[0032] In another embodiment, a formed hole portion 46 (FIG. 9) isformed through the thin film material 36 to create the material passageregion 43. The formed hole portion 46 is generally cone shaped andextends above the thin film material 36. In one example, the formed holeportion 46 has an inner diameter of about 0.025 in. (0.635 mm) andextends above the thin film material 36 about 0.015 in. (0.381 mm).

[0033] The thin film material 36 is then placed into a molding tool 50(FIG. 7). The preferred embodiment of the molding tool 50 includes afemale side 52 having keycap mold cavities 54 and a male side 56 havinganchor mold cavities 58. Although only one set of cavities 54, 58 isshown, the molding tool 50 preferably includes cavities 54, 58 for eachof the keycaps 26 to be molded onto the retainer sheet 20. The keycapmold cavities 54 and the anchor/actuator mold cavities 58 can havedifferent shapes and sizes depending on the shapes of the keycaps 26 andtactile features to be actuated. The molding tool 50 also includesinjection passageways 60 and gates 62 that extend into the respectivekeycap mold cavities 54. Other embodiments of the molding tool 50 arealso contemplated.

[0034] The thin film material 36 is placed in the molding tool 50 suchthat each hole 42 is positioned between a respective keycap mold cavity54 and anchor/actuator mold cavity 58. Each gate 62 preferably pushes atleast one of the flaps 44 b open to form the material passage region 43that receives the gate 62 (i.e., with the flap 44 b acting as a gatedoor). The flap 44 b preferably forms an angle a with respect to theretainer sheet 20 in the range of about 300 to 120°, and most preferablyabout 45°.

[0035] The molding material (e.g., plastic) is then injected througheach injection passageway 60 and gate 62 and flows into each keycap moldcavity 54. The molding material fills the keycap mold cavity 54, passesthrough the hole 42 in the thin film material 36, and fills theanchor/actuator mold cavity 58 surrounding the edges 45 of the thin filmmaterial 36 around the hole 42. The molding material also flows aroundthe flaps 44 to create the retainer anchor portions 32.

[0036] In another embodiment shown in FIG. 10, the flap 44 a has thesame orientation as the flap 44 b (i.e., flap 44 a facing flap 44 b). Inthis embodiment, the molding material flows under the flap 44 a toprevent the flap 44 a from folding downward during the molding process.

[0037] When the molding material hardens, the female side 52 and maleside 56 of the molding tool 50 are removed. In this embodiment, the gatetear away 66 is preferably within the body of the keycap 26 and excessmaterial is removed from the location of the gate tear away 66. Flashingis also removed from the keycaps 26. The keycap anchor/actuator portion30 extends below the retainer sheet 20 and is secured against the bottomsurface 24 of the retainer sheet 20. In this embodiment, the flaps 44are molded within the keycap 26 to form the retainer anchor portions 32.

[0038] In an alternative embodiment, the formed hole portion 46 (seeFIG. 9) can be molded within the keycap 26. In this embodiment, themolding material flows into the cone of the formed hole portion 46 toform an anchor portion or rivet.

[0039] The thin film keypad 10 can then be decorated with numerousfinishing techniques, such as metal plating, painting, screen or padprinting and laser etching. Other decorating options are alsocontemplated. Because the decoration is provided directly on the keycaps26 after the molding, and the thin film is not stretched, the keypadsmade according to the present invention retain graphic quality.

[0040] After the molding operation, the outline of the retainer sheet 20is cut from the thin film material 36, for example, using a die cutoperation. Also, one or more additional holes 68 can be cut in theretainer sheet 20. Although the preferred method cuts the outline of theretainer sheet 20 as the final die cut operation, the outline can alsobe cut prior to the molding operation. The thin film keypad 10 madeaccording to the method described above can then be assembled into anelectronic device.

[0041] In one example, the keycap 26 has a length of about 7 mm long anda width of about 2.5 mm wide. The method of the present invention allowsthe keycaps 26 to be molded with a relatively unlimited height (ascompared to the IMD process). In one example, the height of the keycaps26 can be in the range of about 1.5 mm to 10 mm. The exemplary keycapanchor/actuator portion 30 has a diameter of about 0.061 in. (1.5 mm),although the designer may adjust this dimension to meet actuationrequirements of design and substrates to be actuated. Other dimensionsof the keycaps 26 are also within the scope of the present invention.

[0042] Accordingly, the thin film keypad of the present invention isable to meet the small size requirements of current electronic deviceswhile providing keycaps that are securely mounted.

[0043] Modifications and substitutions by one of ordinary skill in theart are considered to be within the scope of the present invention,which is not to be limited except by the following claims.

The invention claimed is:
 1. A thin film keypad comprising: a retainersheet made of a thin film material and having a top and bottom surface,said retainer sheet including: at least one hole extending through saidthin film material; and at least one retainer anchor portion formed froma portion of said thin film material extending upwardly from said topsurface; and at least one keycap molded onto a top surface of saidretainer sheet and around said retainer anchor portion, said keycapincluding a keycap anchor portion molded through said hole in said thinfilm material such that said keycap anchor portion and said retaineranchor portion mechanically secure said keycap to said retainer sheet.2. The thin film keypad of claim 1 wherein said thin film material is aplastic material.
 3. The thin film keypad of claim 1 wherein said thinfilm material is selected from the group consisting of a polycarbonatematerial and a polyester material.
 4. The thin film keypad of claim 1wherein said thin film material has a thickness in a range of about0.005 in. to 0.010 in.
 5. The thin film keypad of claim 1 wherein saidthin film material has a thickness of about 0.005 in.
 6. The thin filmkeypad of claim 1 wherein said keycap is made of a plastic material. 7.The thin film keypad of claim 1 wherein said keycap is made of amaterial selected from the group consisting of polycarbonate,polycarbonate/ABS blend, and ABS.
 8. The thin film keypad of claim 1wherein said keypad is used in an electronic device, and said keycapanchor portion is configured to be an actuator.
 9. The thin film keypadof claim 1 wherein said keycap is made of an ABS material, and whereinsaid thin film material is a polycarbonate material.
 10. The thin filmkeypad of claim 1 wherein said keycap anchor portion is secured againstsaid bottom surface of said retainer sheet.
 11. The thin film keypad ofclaim 1 wherein said retainer anchor portion includes a flap cut outfrom said thin film material.
 12. A thin film keypad comprising: aretainer sheet made of a thin film material and having a top and bottomsurface, said retainer sheet including a plurality of keycap attachmentregions; and a plurality of keycaps molded onto a top surface of saidretainer sheet at respective said keycap attachment regions, whereinsaid keycaps are molded around portions of said thin film material suchthat said keycaps are mechanically secured to said retainer sheet. 13.The thin film keypad of claim 12 wherein said retainer sheet includesholes extending through said thin film material at said keycapattachment regions, and wherein said portions of said thin film materialaround which said keycaps are molded include edges of said thin filmmaterial around said holes.
 14. The thin film keypad of claim 12 whereinsaid portions of said thin film material around which said keycaps aremolded include flaps cut out from said thin film material and extendingupwardly from said top surface.
 15. The thin film keypad of claim 12wherein said thin film material is a plastic material.
 16. The thin filmkeypad of claim 12 wherein said thin film material is selected from thegroup consisting of a polycarbonate material and a polyester material.17. The thin film keypad of claim 12 wherein said thin film material hasa thickness in a range of about 0.005 in. to 0.010 in.
 18. The thin filmkeypad of claim 12 wherein said thin film material has a thickness ofabout 0.005 in.
 19. The thin film keypad of claim 12 wherein said keycapis made of a plastic material.
 20. The thin film keypad of claim 12wherein said keycap is made of a material selected from the groupconsisting of polycarbonate, polycarbonate/ABS blend, and ABS.
 21. Thethin film keypad of claim 12 wherein said keycap is made of an ABSmaterial, and wherein said thin film material is a polycarbonatematerial.
 22. A method of making a thin film keypad comprising: formingat least one keycap attachment region on a thin film material, each saidkeycap attachment region including at least one molding material passageregion; placing said thin film material into a molding tool having atleast one keycap mold cavity such that each said molding materialpassage region is located within each said keycap mold cavity,respectively; injecting a molding material through said molding materialpassage region in said thin film material and into said keycap moldcavity such that at least one keycap is molded onto a top surface ofsaid thin film material, and wherein said molding material flows arounda portion of said thin film material such that said keycap ismechanically secured to said thin film material.
 23. The method of claim22 further including cutting an outline of a retainer sheet from saidthin film material such that said keycap is molded onto said retainersheet.
 24. The method of claim 22 wherein said molding material isselected from the group consisting of polycarbonate, polycarbonate/ABSblend, and ABS.
 25. The method of claim 22 wherein said thin filmmaterial is selected from the group consisting of a polycarbonatematerial and a polyester material.
 26. The method of claim 22 whereinforming each said keycap attachment region includes forming at least onehole through said thin film material, and wherein said retainer sheet isplaced in said molding tool with said hole positioned between saidkeycap mold cavity and an anchor mold cavity such that said moldingmaterial flows through each said hole and around an edge of said thinfilm material.
 27. The method of claim 22 wherein forming said keycapattachment region includes cutting at least one flap from said thin filmmaterial to form said material passage region, and wherein said moldingmaterial flows around each said flap.
 28. The method of claim 27 whereinsaid molding tool includes a gate for injecting said molding material,and wherein inserting said retainer sheet into said molding toolincludes inserting said gate through said material passage region suchthat said gate moves said flap into said keycap mold cavity.
 29. Amethod of making a thin film keypad comprising: forming a plurality ofkeycap attachment regions on a thin film material, each of said keycapattachment regions including at least one hole and at least one materialpassage region; placing said thin film material into a molding toolincluding a female side having keycap mold cavities and a male sidehaving anchor mold cavities, wherein said retainer sheet is positionedsuch that said holes are located between respective said keycap moldcavities and said anchor mold cavities and such that said materialpassage regions are located within respective said keycap mold cavities;and injecting a molding material through said material passage regionsin said thin film material and into said keycap mold cavities, whereinsaid molding material flows through said holes and into said anchor moldcavities such that keycaps are molded onto a top surface of said thinfilm material and are mechanically secured to said thin film material.30. The method of claim 29 wherein said thin film material is selectedfrom the group consisting of a polycarbonate material and a polyestermaterial, and wherein said molding material includes ABS.
 31. The methodof claim 29 wherein forming said material passage regions includescutting flaps from said thin film material, wherein said male side ofsaid molding tool includes gates for injecting said molding material,and wherein inserting said thin film material into said molding toolincludes inserting said gates through respective said material passageregions such that said gates move respective said flaps into respectivesaid keycap mold cavities and said molding material flows around saidflaps.
 32. The method of claim 29 wherein forming said material passageregions includes forming formed hole portions from said thin filmmaterial, wherein said male side of said molding tool includes gates forinjecting said molding material, and wherein inserting said thin filmmaterial into said molding tool includes inserting said gates throughrespective said material passage regions such that said molding materialflows around said formed hole portions.
 33. The method of claim 29further including cutting an outline of a retainer sheet from said thinfilm material such that said keycaps are molded onto said retainersheet.